1. Field of the Invention
The present invention relates to a reciprocating piston type refrigerant compressor provided with a refrigerant gas suction mechanism improved so as to increase the volumetric compression efficiency thereof.
2. Description of the Related Art
Various reciprocating piston type refrigerant compressors such as a swash plate operated reciprocating piston type refrigerant compressor, and a wobble plate operated reciprocating piston type refrigerant compressor are known.
Japanese Unexamined Patent Publication (KoKai) No. 3-92587 (JP-A-3-92587) discloses a typical conventional swash plate operated reciprocating piston type refrigerant compressor provided with a cylinder block having a plurality of axial cylinder bores in which pistons are axially reciprocated in response to the nutation of a swash-plate about the axis of rotation of its drive shaft. The swash-plate is housed in a swash plate chamber centrally formed in the cylinder block. The swash-plate chamber is also used for receiving refrigerant gas when it returns from the external refrigeration circuit.
The above-mentioned compressor is further provided with flapper type suction valves which are used to open and close suction ports arranged between respective compression chambers defined by the reciprocating pistons in the cylinder bores and a pair of suction chambers (the front and rear suction chambers) for receiving the refrigerant gas before compression, and fluidly communicated with the above-mentioned swash plate chamber via suction passageways. The refrigerant gas before compression is drawn into respective compression chambers through the suction ports via the opening flapper type suction valves during the suction stroke of respective reciprocating pistons moving from the top dead center to the bottom dead center thereof. When respective reciprocating pistons implement the compression and discharge stroke thereof by moving from the bottom dead center to the top dead center thereof in the cylinder bores, respectively, the flapper type suction valves are closed. The refrigerant gas is compressed in the compression chamber, and discharged therefrom into a pair of discharge chambers (the front and rear discharge chambers) via the opening flapper type discharge valves which arranged so as to open and close discharge ports formed between the compression chambers and the discharge chambers.
The opening and closing of the flapper type suction valves are caused by a pressure differential between the suction chambers and respective compression chambers in the cylinder bores. Namely, when pressure prevailing in the suction chambers is higher than that in the compression chambers due to the suction stroke of the reciprocating pistons, the flapper type suction valves are bent by the pressure differential to move toward the opening position thereof opening the suction ports.
Since the flapper type suction valves are made of elastic material to show resilience when bending, such resilience of the flapper type suction valves acts as an elastic resistance against movement of respective suction valves. Accordingly, the opening of the flapper type suction valves does not occur before the above-mentioned pressure differential between the suction chambers and the compression chambers becomes larger than a predetermined level. Thus, the motion of opening of the flapper-type valves cannot be quick enough for achieving an instant suction of the refrigerant gas into the compression chambers.
Further, the above-described piston type compressors are generally supplied with a lubricating oil in the form of oil mist suspended in the refrigerant gas in order to lubricate the internal elements of the compressor. Thus, the lubricating oil suspended in the refrigerant gas is distributed to many of the internal portions of the compressor by flowing together with the refrigerant gas. As a result the lubricating oil, suspended in the refrigerant gas as an oil mist, can be carried toward and attach to faces of the flapper type suction valves as well as wall portions surrounding the suction ports and contacted by the flapper type suction valves. Thus, when the lubricating oil attaches to the flapper type suction valves and the wall portions surrounding the suction ports, it is so viscous as to prevent quick opening of the flapper type suction valves from the closing position thereof contacting the wall portions. Accordingly, the quick opening of the flapper type suction valves is prevented due to the attachment of the lubricating oil to both the flapper-type suction-valves and the wall portions.
Since the flapper type suction valves of the conventional refrigerant compressor are not able to open quickly in response to a pressure differential between the suction chambers and the compression chambers, the amount of flow of the refrigerant gas from the suction chambers into the compression chambers is reduced, and accordingly, the volumetric efficiency in the compression of the refrigerant gas by the conventional reciprocating piston type refrigerant compressor using the flapper type suction valves is made small. Furthermore, when the flapper type suction valves are opened so as to permit suction of the refrigerant gas into the compression chambers, the resilience of the suction-valves per se acts as resistance against the suction of the refrigerant gas, and thus, the amount of suction of the refrigerant gas is further reduced.
In the described conventional swash plate operated reciprocating piston type compressor, the plurality of axial cylinder bores of the cylinder block are arranged around the axis of rotation of the drive shaft with an equiangular distance between the two neighboring cylinder bores. Nevertheless, when the angular distance between the two neighboring cylinder bores is set small, the thickness of a separating rigid portion between the two neighboring cylinder bores is reduced to thereby weaken the physical strength of the cylinder block. Moreover, when the suction passageways for the refrigerant gas flow from the swash plate chamber to the suction chambers are provided in the separating rigid portions as disclosed in JP-A-3-92587, the formation of such suction passageways will further weaken the physical strength of the cylinder block.
When the angular distance between the two neighboring cylinder bores is set large to obtain a thick separating rigid portion in the cylinder block, respective cylinder bores must be arranged along a circle having a large radius about a center lying in the axis of rotation of the drive shaft. Therefore, such large radius of the circle along which the cylinder bores are arranged will bring about an increase in the physical size of the compressor.
Nevertheless, when the radius of the circle along which the cylinder bores are arranged is made small to reduce the diametrical size of the cylinder block, the angular distance between the two neighboring cylinder bores must be necessarily reduced, and accordingly, the circumferential thickness of respective rigid portions between the two neighboring cylinder bores is reduced to thereby weaken the physical strength of the cylinder block, as described before. Consequently, it is difficult to reduce the size of the compressor.
In addition, the provision of the suction passageways in the rigid portions between the two neighboring cylinder bores of the cylinder block is apt to cause loss of pressure of the compressed refrigerant gas, and accordingly, the compression efficiency of the compressor is further reduced. A reciprocating piston type compressor is described in copending U.S. Application Ser. No. 08/103,888 in which volumetric compression efficiency is significantly improved. In the compressor described therein, a rotary valve is mounted on a drive shaft. A suction passageway for introducing refrigerant gas into compression chambers in associated cylinder bores is formed in the rotary valve. A circumference of the rotary valve is axially slanted. An inner wall of a receiving chamber which accommodates the rotary valve is also axially slanted. The rotary valve is slidable along the axial direction. Air tight sealing between the outer circumference of the rotary valve and the inner wall of the receiving chamber is effectively achieved by urging the rotary valve from a large diameter side to a small diameter side thereof. The compression chambers successively communicate with the suction passageway synchronously with reciprocal motion of pistons which results in rotation of he rotary valve.
However, since most of the area of the outer circumference of the rotary valve is consistently urged against the inner wall of the receiving chamber in the compressor, the lubricant oil that is mixed with the refrigerant gas may not be sufficient to adequately lubricate the slidably contacting portion therebetween. Inadequate lubrication prevents smooth rotation of the rotary valve and may result in excessive wear or even catastrophic failure.